Exploring the early stages of high-energy heavy-ion collisions

Dr. Soeren Schlichting
Junior Professor
Fakultät für Physik
Universität Bielefeld

Over the past decades experiments at the Relativistic Heavy-Ion Collider (RHIC) and the Large Hadron Collider (LHC) have discovered the formation of a de-confined Quark-Gluon Plasma (QGP) , and established a standard picture of the space-time evolution of the QGP based on relativistic viscous hydrodynamics. While high-energy heavy-Ion collisions thus provide a unique laboratory to study QCD matter under extreme conditions, it has proven challenging to understand how the far-from equilibrium matter created in the collision turns into a nearly equilibrated plasma of quarks and gluons. Starting with a general introduction to the physics of heavy-ion collisions, I will highlight recent theoretical progress in understanding thermalization mechanisms in QCD plasmas and address the question how an almost equilibrated Quark-Gluon plasma is created during the early stages of high-energy collisions. I will also discuss how these studies provide new insights into the range of applicability of dissipative fluid dynamics and how the out-of-equilibrium dynamics of the QGP can be explored in more detail in future experiments at RHIC and LHC.…

Green function approach to R-matrix theory and applications to light nuclear reactions

Dr. Mark Paris
Staff Member, Los Alamos National Laboratory

We analyze reactions of neutrons and charged-particles (p,d,t,h,a) on light elements (A < ~ 20). Our primary tool in this endeavor is the Green function of the Schroedinger equation, with boundary conditions prescribed at finite channel radii, in the phenomenological R-matrix approach. We review some elements of reaction theory in the R-matrix approach context and emphasize the multichannel unitarity of the formalism, which is essential to accurate phenomenological parametrization of the scattering and reaction observables. R-matrix parameters are related to various resonance-parameter representations and we discuss the analytic structure of the T-matrix amplitudes as a function of complex energy. Uncertainty quantification of the resulting observables is given. Several examples of R-matrix evaluations of light compound systems (NN, ⁵…

Zooming in on CGM microphysics

Prof. Peng Oh
Department of Physics
UC Santa Barbara

Galaxy halos are fantastic laboratories for the physics of diffuse plasmas, where physical ingredients such as turbulence, magnetic fields, cosmic rays, thermal instability, and many more play out on grand scales. The results have important implications for gas inflow which fuels star formation, as well as associated feedback and recycling processes. I describe recent progress on understanding the microphysics of the circumgalactic medium via high-resolution, idealized simulations which are complementary to cosmological simulations of galaxy formation. I describe numerical experiments on the interaction between turbulence and cooling, which bears on the survival of cold clouds in galactic winds, with special attention to the resolution required for key physical processes. Cold clumps robustly have a power-law distribution in size; I will discuss some ideas on the origin of such power-law distributions. …

Relaxed relaxation

Dr. Hyungjin Kim
DESY, Germany

Cosmological relaxation of electroweak scale has been proposed as a solution to the hierarchy problem. In the early universe, Higgs mass is scanned by an axion-like particle, relaxion, and it is naturally relaxed to the electroweak scale via a certain feedback loop. After a brief introduction to the relaxion scenario, I will discuss that not only the Higgs mass but also the relaxion mass is relaxed to a parametrically smaller value through the same mechanism. This has interesting phenomenological implications as low energy observers might find the relaxion parameters fine-tuned although the mechanism itself is constructed in a technically natural way. I will show that the relaxion coupling constants to the standard model particle could be a few orders of magnitude larger than ‘natural’ values of coupling constants in Higgs portal models. I will also discuss implications of various experiments in different physic frontiers to the relaxed relaxion model as well as its dark matter phenomenology.…

Mini Break Day

No classes or meetings can be scheduled.…

The MONICA Detector and Future Plans for AMS at AGFA

Lauren Callahan
Graduate Student, University of Notre Dame

Experimentalists in the field of Accelerator Mass Spectrometry (AMS) are constantly looking for ways to separate higher mass isobars to better understand the origins of the universe. Through the use of the Argonne Gas-Filled Analyzer (AGFA) and Argonne National Lab (ANL), these AMS measurements have a better chance of success due to the high energies achieved by the accelerator at ANL and AGFA’s higher magnetic rigidity. To aid in the success of AMS at AGFA, a new detector, the Multi-anOde Nuclear Ionization Chamber at Argonne (MONICA) was constructed at the Hebrew University of Jerusalem and commissioned at the Notre Dame Nuclear Science Lab. A previous AGFA experiment providing proof of concept for an AMS experiment, commissioning measurements of the MONICA detector, and future plans for the detector will be discussed.…

The Astrophysical Context of Gravitational Wave Events

Dr. Mohammadtaher Safarzadeh
Postdoctoral Fellow in Theoretical Astrophysics
UC Santa Cruz / Harvard

We live in an era of breakthrough discoveries in gravitational waves (GW) astronomy. Every month or so, such discoveries by LIGO/Virgo have been making headlines because these events’ nature has been far from the expectations. But why are we puzzled? And what is the road ahead for us to a deeper understanding? I discuss two of the puzzling events that LIGO has discovered: 1) The most massive binary black hole merger with masses above the pair-instability limit. After a deep dive into the physics of pair-instability supernova, I will discuss how a broader perspective on the host environment of binary black holes can hold the key to understanding the nature of such massive systems. 2) The most massive binary neutron star merger. I will present possible scenarios to explain why we have not detected such systems in the radio observations before and how the key to understanding these events might lie in the r-process enrichment in the early universe and magnetic field evolution of neutron stars. Through these two examples, I will conclude that the synergy of traditional electromagnetic-wave astronomy with gravitational wave astronomy is essential for gaining insights into the surprises that are being uncovered with these new observations.…

Title and abstract forthcoming

Dr. Daniel Weigand
Postdoctoral Researcher
Argonne National Laboratory

Hosted by Prof. Tsai

All interested persons are invited to attend remotely—email physics@nd.edu for information.…

Title and abstract forthcoming

Prof. Louise Edwards
California Polytechnic State University

All interested persons are invited to attend remotely—email physics@nd.edu for information.…

Title and abstract forthcoming

Dr. Xilu Wang
University of Notre Dame

Hosted by Prof. Surman

All interested persons are invited to attend remotely—email physics@nd.edu for information.…